ABSTRACT Hyperthermia induced by magnetic nanoparticles in high frequency alternating magnetic fields (AMF), or Magnetic Fluid Hyperthermia (MFH), is based on the delivery of thermal energy at the nano-scale to tumors using iron oxide based magnetic nanoparticles (MNP) and an externally applied AMF. This phenomenon is the result of particle rotation or movement of the magnetic dipole. The fact that energy is only dissipated under high-frequency and moderate amplitude fields that can be constrained to the tumor region make MFH a highly promising form of non-invasive, externally activated cancer treatment To this date, the prevailing paradigm in the field is that delivery of nanoscale particles to tumors can be achieved by passive targeting due to the enhanced permeation and retention (EPR) effect. However, in vivo experiments tumors suggest otherwise, thus, posing potential limitations on the successful translation of such systems to the clinic. The aforementioned discrepancy reveals a need to understand the in vivo spatial and temporal behavior of nanoparticles as a result of their surface physicochemical properties. To our knowledge, the relationship between surface properties and the resulting temporal and spatial behavior has not been investigated in orthotopic mouse models of cancer. The long-term goal of this project is to develop MNPs as a clinically feasible tool by providing a comprehensive understanding from fundamental particle design to clinical application. The main objective of this proposal is to pursue the optimization ofthe spatial and temporal behavior of Magnetic Nanoparticle Heaters (MNH) and perform an in vivo efficacy assessment of targeted or intelligent (iMNHs) developed in our laboratories forcancer treatment applications. Otyr working hypothesis is that long circulating maonetic nanoparticles withspecific targeting ligands, IMNH, will improve nanopartide delivery to ovarian orthotopic tumors, which willresult in improved therapeutic outcome. This hypothesis was based on preliminary data derived during the pilot project phase, which demonstrated: (1) in vivo nanoparticle's temporal behavior is governed by surface properties, (ii) passive targeting due to the EPR effect may not be sufficient to deliver sufficient particles to the tumor site, and (iii) intelligent targeted nanoparticles have demonstrated significant improvements in treatment efficacy in vitro. The rationale for the proposed research is that once the pharmacokinetics, biodistribution, therapeutic efficacy, and, safety ofthe proposed systems is assessed and understood, future steps can be taken to optimize system's properties thus improving its clinical potential.